Sunlight is known to lower blood pressure, but now a team of British researchers has figured out why.

What they found is that nitric oxide stored in the top layers of the skin reacts to sunlight and causes blood vessels to widen as the oxide moves into the bloodstream. That, in turn, lowers blood pressure, Health Daily reported.

"This is an unexpected finding, in that the skin has not been considered to be involved in blood pressure regulation," said lead researcher Martin Feelisch, a professor of experimental medicine and integrative biology at the University of Southampton.

Feelisch said he thinks exposure to ultraviolet light might help reduce the risk for heart disease. "That's where it becomes interesting," he said.

Among people with normal blood pressure, the effect of ultraviolet light is modest, a drop in blood pressure of between 2 and 5 millimeters of mercury (mmHG), Feelisch said. "This is a mild effect," he said. "But if you repeat this study in people with high blood pressure, I would predict you will see a more substantial drop."

Avoiding sunlight or using sun block constantly out of a fear of skin cancer could be a new risk factor for heart disease, Feelisch said. He isn't suggesting that people should sunbathe or use tanning beds in hopes of lowering blood pressure, however. What he recommended is spending a moderate amount of time outdoors.